Plants small
trees or shrubs, sometimes trailing or climbing but not twining (anchored to
the substrate by adventitious roots). Twigs 4-angled or sometimes circular in
cross-section, sometimes with corky wings. Leaves opposite, deciduous or
partially to completely evergreen, short-petiolate. Leaf blades variously ovate
to elliptic or obovate, the margins entire or finely toothed, the surfaces
glabrous or inconspicuously hairy. Inflorescences axillary clusters or small
panicles or the flowers occasionally solitary in the leaf axils. Flowers
usually perfect (rarely functionally staminate or pistillate). Sepals 4 or 5,
fused toward the base. Petals 4 or 5. Stamens 4 or 5, these inserted along the
margin of the nectar disk, the filaments minute (0.1–0.5 mm). Ovary
usually with 1–5 locules and 2–6 ovules per locule. Style
short, stout, the stigma entire or shallowly 3-lobed. Fruits ovoid or more or
less globose, sometimes (2)3–5-lobed, pink to red, dehiscent by
(2)3–5 valves. Seeds ovoid to ellipsoid, 1 or 2(–6) per locule,
brown, each enclosed in a fleshy red to orange aril. About 130 species, nearly
worldwide.

The taxonomy of Euonymus
has been somewhat confused. There is considerable variation in growth habit and
leaf characters, with many variants sometimes receiving separate names and
numerous species described from horticultural selections of Asian origin. Many
of these problems, especially those concerning the Oriental species, were
addressed by Ma (2001), who reduced the number of accepted species from 200 or
more to 129.

The generic name
Euonymus has engendered a lot of controversy. Linnaeus (1753) spelled it
“Evonymus” in his Species Plantarum and “Euonymus” in his Genera
Plantarum (Linnaeus, 1737). After decades of debate (Zijlstra and Tolsma,
1991), the spelling Euonymus was conserved at the International
Botanical Congress in Tokyo in 1993. Also, Linnaeus (1753) treated Euonymus
and its species with a masculine (-us) ending, but the classical Greek
root is considered feminine. After decades of inconsistent species-epithet
endings, Paclt (1998b) made a formal proposal to conserve the name as feminine
(with -a rather than -us) for the species epithets. However, the Committee
for Spermatophyta of the International Association of Plant Taxonomy, which
must approve such proposals before they can be voted upon at an International
Botanical Congress, chose not to favor Paclt’s view (Brummitt, 2000). The
generic name (and thus specific epithets) therefore must be treated as
masculine.

Polyembryony has
been reported in E. americanus and E. alatus (Brizicky, 1964a).
The seeds of these species contain up to nine embryos, many of them small and
apomictic. Only two chromosome levels, 2n=32 and 2n=64, have been
reported for Euonymus, the latter possibly arising following past
interspecific hybridization (Nath and Clay, 1972). Several species of Euonymus
are prized for their colorful fall foliage and attractive fruits with bright red
arillate seeds. Although sometimes used in folk medicine, the bark and fruits
generally are considered poisonous.